Mapping of snail intermediate host habitat reveals variability in schistosome and nonschistosome trematode transmission in endemic settings

• Type of Material: Article
• Authors: Teckla Angelo, National Institute for Medical Research; Naima Starkloff, Emory University; Moses Paul Mahalila, National Institute for Medical Research; Jenitha Charles, National Institute for Medical Research; David Civitello, Emory University; Safari Kinung'hi, National Institute for Medical Research
• Language: English
• Date: 2023-06-06
• Publisher: Cold Spring Harbor Laboratory
• Publication Version: Preprint (Prior to Peer Review)
• Copyright Statement: The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.
• License: Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International
• Final Published Version (URL): https://doi.org/10.1101/2023.06.04.543635
• Title of Journal or Parent Work: bioRxiv
• Keywords: environmental interventions; waterbodies; human exposure; schistosome parasite distribution; schistosomiasis transmission; drug administration; snails
• Research Categories: Biology, Ecology; Health Sciences, Pathology

Abstract

Background There is growing recognition that mass drug administration must be complemented with environmental interventions to interrupt schistosomiasis transmission. Accurate mapping of snails and schistosome parasite distribution is critical to identify foci of human exposure and prioritize sites for interventions. Methodology We conducted longitudinal environmental surveys of snails and schistosomes in 467 waterbodies across 86 villages in northwestern Tanzania to describe spatial and temporal variation in snail and schistosome parasites presence and identify relevant underlying predictors. We conducted time constrained net sampling of Bulinus snails from vegetation, sediments, and floating objects and then examined all collected snails for patent infections. Principal findings A total of 43,272 Bulinus snails were collected across the three visits to each waterbody spanning November 2020 – August 2021, and we conducted statistical analyses on the latter two visits with more in-depth surveys (25,052 snails). We found patent schistosome infections in 0.87% of snails, 9.8% of waterbodies, and 31% of villages in all six districts. Variance decomposition indicated that variation among waterbodies was associated with variation in snail presence and the prevalence of schistosomes and nonschistosome parasites, whereas variation among villages and districts was not. Snail presence was highest in March-May a period of heavy rains, but otherwise not associated with waterbody characteristics. Waterbodies permitting cattle use had significantly higher prevalence of schistosomes than those permitting only human use. Nonschistosome parasites were more prevalent in June to September the dry season but were not associated with other waterbody characteristics. Waterbody permanence and distance to the nearest primary school were not associated with snails or parasites. Conclusions/significance This study revealed substantial variation in snails, schistosome and nonschistosome abundance at local (waterbody) scales, and it suggests links between community-driven water use decisions and schistosome transmission. The identification of local drivers of snail and schistosome abundance level and transmission factors at waterbody scale can complement studies across larger scales to shed light on transmission hotspots and guide the development of targeted interventions for schistosomiasis control.